1. Field of the Invention
The present invention relates to a fuse structure used in an integrated circuit device, and more particularly, to a novel fuse structure that can prevent the adjoining fuse structure from being damaged in the laser blow process.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC), and in particular in memory devices as elements for altering the configuration of the circuitry contained therein. As such, memories are commonly built which programmed capabilities wherein fuses are selectively xe2x80x9cblownxe2x80x9d by, e.g., a laser beam.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, wherein when any of these spare elements fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements is accomplished by fuses which are blown (i.e., melted away) when required, preferably, by the laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used both in the memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability have been problematic in most conventional fuse designs.
FIG. 1 is a cross-section of a traditional fuse structure. FIG. 2 is a top view of a traditional fuse structure. And FIG. 1 shows the cross section C-Cxe2x80x2 of FIG. 2.
Referring to FIG. 1, symbol 100 shows an insulated layer substrate. A metal layer M0 is formed on part of the substrate 100. An oxide layer 120 is formed on the metal layer M0 and part of the substrate 100. A metal layer M1 having an optimal position of laser spot 110 is formed on part of the oxide layer 120. At least one conductive plug 130 is defined through the oxide layer 120, for electrically connecting the M0 layer and the M1 layer. A fuse window 140 is formed above part of the M1 layer comprising the position 110 and part of the oxide layer 120. Symbol 150 shows a passivation layer.
In FIG. 2, there are plural fuse structures 210, 220, 230 in the fuse window 140. Each fuse structure 210, 220, 230 comprises the M0 layer, the plug 130 and the M1 layer. The solid line area shows the M1 layer, the dash line area shows the M0 layer, and each structure 210, 220, 230 comprises its own optimal position of laser spot 110. To give an example, a laser beam 290 blows the position 110 of the fuse structure 220. Because of misalignment of the laser beam 290 or thermal scattering of the laser beam 290, this laser blow process can damage the M0 layer of the fuse structures 210, 230 which near the fuse structure 220 by thermal shock. This causes the fuse structures 210, 230 to crack, and seriously affect device reliability and yield.
An object of the present invention is to provide the first fuse structure. An optimal position of laser spot is defined above a substrate. A first conductive layer is formed on part of the substrate. A dielectric layer is formed on the substrate and the first conductive layer. A second conductive layer comprising the position of laser spot is formed on part of the dielectric layer. A third conductive layer is formed on the part of the dielectric layer placed above the first conductive layer, where the third conductive layer is insulated from the first and second conductive layers. At least one conductive plug penetrates the dielectric layer, to electrically connect the first conductive layer and the second conductive layer.
The second fuse structure of the present invention is also provided. An optimal position of laser spot is defined above a substrate. A first conductive layer is formed on part of the substrate. A dielectric layer is formed on the substrate and the first conductive layer. A second conductive layer comprising the position of laser spot is formed on the dielectric layer. At least one conductive plug penetrates the dielectric layer, to electrically connect the first conductive layer and the second conductive layer.
The present invention improves on the prior art in that the third conductive serving as a floating layer is placed above the first conductive layer; or the second conductive layer is expanded above the first conductive layer. Thus, the invention can prevent both misalignment of the laser beam and thermal scattering of the laser beam from damaging the first layer of the fuse structure in the laser blow process, raises reliability and yield, and ameliorates the disadvantages of the prior art.